LONDON - The global rate of tuberculosis infections has leveled off, public health officials said Thursday, offering a glimmer of hope for the first time since the disease's spread was declared a global emergency more than a decade ago.

But despite that good news, an ominous threat is emerging from drug-resistant versions of TB and the potential for its spread with the help of the AIDS epidemic. The AIDS virus weakens the immune system making people more susceptible to TB, and health experts are worried that will propel it across Africa.

The latest statistics on tuberculosis, issued in a new report Thursday from the World Health Organization, showed there were 136 TB cases per 100,000 people worldwide in 2005, the most recent figures available. That compares with 136.5 cases the previous year.

"This is a breakthrough," said Dr. Marcos Espinal of WHO's Stop TB Partnership. "It's the first time we've had good news about the epidemic since 1993."

In Africa, the TB rate was 343 cases per 100,000, more than twice the global rate, indicating the continuing challenge there.

And while the global rate remained steady, the actual number of people with TB increased because of population growth. In 2005, there were 8.8 million new tuberculosis cases, and 1.6 million deaths, the WHO said.

Increasing numbers of drug-resistant tuberculosis cases, including the emergence of a deadly version of the disease, known as extensively drug-resistant tuberculosis or XDR-TB, also have complicated efforts to control tuberculosis. XDR-TB is resistant to most drugs commonly used to treat tuberculosis.

In Africa, XDR-TB has only been reported in South Africa - which has detected more than 300 cases, with about 30 new cases every month. Experts said they suspect it is present, but undetected, in other African countries with weaker surveillance systems.

The deadly drug-resistant form has also appeared in wealthy countries, with cases reported in all Group of Eight industrialized nations. In the United States, which reported an all-time low for TB cases with 4.6 per 100,000 people, there were just two cases of the extensively drug-resistant form reported in 2006. (The United States has more recent figures than WHO.)

However, lack of access to existing treatments are a bigger killer worldwide than drug-resistant strains, experts said.

"Most people have tuberculosis that is sensitive to the drugs we use, but will die because of the failure to access the very simple, cheap treatment that we've been using for the last 40 years," said Dr. Tom Ellman, a health adviser for the medical aid group Medecins Sans Frontieres, also known as Doctors Without Borders.

Another problem is antiquated means of diagnosing and treating the disease.

"Progress in tuberculosis research reads like a history book," said Dr. Dermot Maher, a WHO disease expert. The last effective TB drug was discovered more than 50 years ago and takes about six months to improve patients' health.

The standard diagnosis involves a century-old test in which lab technicians search for the bacteria under a microscope, and it misses up to half of all active infections. Determining whether the strain is drug-resistant can take up to two months - and if the patient also has AIDS, they could be dead by the time the results are in.

Although tuberculosis research has had a boost from public-private partnerships and donors such as the Bill and Melinda Gates Foundation, experts believe it will be years before new diagnostics or drugs are available. Raising enough money to fight TB worldwide is also a problem. WHO estimates it needs $1.1 billion for 2007, with Africa facing the biggest funding gap.

To make a serious dent in controlling it, health officials are now working to merge TB and AIDS treatment programs. Of the 40 million people worldwide living with the AIDS virus, one-third are estimated to have tuberculosis. Yet in much of Africa, patients must seek out treatment separately.

"HIV is fueling the tuberculosis epidemic," said Maher. "If we can remove the fire from the flame, the tuberculosis incidence will go down."

Still, it is unclear whether countries are taking the international health community's advice. Medecins Sans Frontieres say that only 3 percent of TB patients in Africa are offered HIV tests.